We will develop mitochondria-targeted antioxidants (MTAs) and imaging probes that will mitigate cardiotoxicity and enhance antitumor efficacies of chemotherapeutic drugs. We will use doxorubicin (DOX), a front-line antitumor agent in breast cancer treatment. DOX causes delayed dose-dependent cardiotoxicity. Clinically, this side effect is managed with conventional antioxidants and iron chelators. This proposal provides a new adjuvant approach in breast cancer chemotherapy. Its genesis is based upon the following discoveries: 1) MTAs (e.g., Mito-Q, a synthetic drug analog of an endogenous antioxidant, Co-enzyme-Q, present in the mitochondrial respiratory chain) inhibit DOX-mediated cardiotoxicity in a preclinical animal model and in cardiomyocytes, and 2) MTAs (Mito-Q and Mito-CP, a nitroxide targeted to mitochondria) cause antiproliferative and cytotoxic effects in breast cancer cells (MCF-7 and MDA-MB-231) but not in non- transformed breast epithelial cells (MCF-10A) and significantly enhance DOX-induced breast cancer cell toxicity. We hypothesize that mitochondria-targeted antioxidants enhance DOX-mediated antitumor effects but attenuate DOX cardiotoxicity. Response to chemotherapy will be monitored by using the mitochondria-targeted technetium-labeled imaging agents (99mTc-Mito10-MAG3) in a chemically-induced breast carcinoma animal model. Specifically, we will: (i) Investigate the cytotoxic effects of MTAs alone and with DOX in breast cancer cells, (ii) Assess the cytotoxic effects of MTAs and DOX in breast cancer cells overexpressing multi-drug resistant protein, (iii) Evaluate the adjuvant chemotherapeutic effects of MTAs and DOX in an in vivo breast cancer model, and (iv) Assess the cardioprotective and oxy-radical scavenging effects of MTAs in DOX- treated cardiomyocytes and in DOX-treated rat cardiomyopathy model. These aims will be accomplished using HPLC-fluorescence and HPLC-electrochemical detection techniques, scintimammography and echocardiography. Abnormal generation of reactive oxygen species will be detected using novel species- and target-specific probes. We will develop innovative MTA-based adjuvant therapy that can be used to inhibit DOX-induced cardiotoxicity. This research may potentially lead to novel ways for improving the therapeutic efficacy of DOX and other antitumor agents used in breast cancer treatment. PUBLIC HEALTH RELEVANCE: The proposed research is clinically relevant in that results obtained from this work will likely mitigate the adverse side effects associated with breast cancer chemotherapy. This work will also enable early detection of breast cancer in an animal model using a novel imaging technique.